Rachel Cooke is impressed by a new series with messed up morals.

The new Showtime series Homeland (Sundays, 9.30pm), for which some of us have been waiting for ages, is really rather good - by which I mean that after only one episode, I'm hooked and desperate to see part two. Is Sergeant Nicholas Brody (Damian Lewis), recently returned from eight years as a prisoner in Iraq, an all-American hero or an al-Qaeda operative? Is Carrie Mathison (Claire Danes), CIA agent extraordinaire, a delusional lunatic or the only person with the wits to have noticed that Brodie has been "turned"?

You have to admit that the set-up is a good one, guessing games being the best way to keep an audience wanting more. OK, so there are - when you think about it - some improbabilities, but this being slick, expensively made American TV, you tend not to notice them until afterwards. If the series was set in Britain, with Mathison living in a flat in Kennington and Brodie and his family stationed in, say, Plymouth, I fear I'd be somewhat less goggle-eyed.

It has its share of clichés, too. In the first episode, Brodie's wife, Jessica, was in bed, writhing ecstatically with her new lover when - dring, dring! - the telephone rang. Why do missing-in-action servicemen always ring at the very moment their wives are enjoying orgasmic sex with their husbands' close friends?

On the other hand, I enjoyed the fact that both Brodie's army superiors and the director of the CIA's counterterrorism centre, David Estes (David Harewood), were more concerned with trundling him in front of the TV cameras than with his health (as his plane from Germany was about to land, he was in the loo throwing up his guts). Believable. Neat, too, that the president was not there to greet his poster boy for the war, only the Veep. Most series would have been unable to resist bringing on the main man. Cue hands on hearts and "The Star-Spangled Banner".

The best thing about it are the two central performances. Damian Lewis is great. I still shiver at the memory of his Soames in ITV's 2002 version of The Forsyte Saga. Lewis has a confidence - possibly born of that posh school he attended - that liberates him wonderfully from the curse of acting-with-a-capital-A, and there is something rodenty about his features that enables him to look sympathetic one moment and utterly weasel-like the next. Danes, meanwhile, has put her character just the right side of irritating (though, with 11 episodes to go, she could easily tip over to the other side). Mathison has a mood disorder and takes anti-psychotic drugs, though her bosses do not know it. Danes plays her just a little twitchy, just a little bug-eyed.

The writers are cleverly messing with morals when it comes to her character. She wants to defend the US from a terrorist attack but her methods are guaranteed to induce queasiness. Where is her empathy? Having installed cameras and bugs in Brodie's house - she did not have her superiors' permission to do this - she sat coolly watching as he entered both his house for the first time in eight years and, a little later, his wife. She is pretty dislikeable: a highly unusual thing for a female lead to be in an American drama. Some will inevitably liken her to the equally dogged Sarah Lund in the Danish series, The Killing.

But where Lund is still and silent, Mathison is jittery and occasionally frantic. I would not want her on my side and it will be interesting to see how this emotional distance plays out several episodes down the line. Will I be rooting for her? Or will I long to see her in an orange prison overall?

As for Brodie, let's hope that his character's plight will come to haunt Homeland addicts. The after-effects of torture aren't pretty. But if he has "turned", will this be presented as a simple, out-and-out act of treason? Or will it be more nuanced than that?

Going over to the "other side" might begin as a survival mechanism. It might also be the result of a particularly clever and heinous kind of torture. If the writers are brave, they will go the grey rather than the black-and-white route (see the very ugly 24, with whom Homeland shares its producers). Fingers crossed they don't wimp out.